Wear resistant articles and facings therefor



United States Patent Donald H. Hall;

Erwin J. Nunlist, Rochester, N.Y. 721,522

Apr. 15, 1968 Dec. 29, 1970 Sybron Corporation Rochester, N.Y.

a corporation of New York Continuation of application Ser. No. 441,624,Mar. 22, 1965, now abandoned Inventors Appl. No. Filed Patented AssigneeWEAR RESISTANT ARTICLES AND FACINGS THEREFOR 5 Claims, 2 Drawing Figs.

U.S. Cl 277/96, 277/88, 277/93 Int. Cl Fl6j 15/54 Field of Search 277/38- 43, 81, 84-88, 92, 93, 935D, 96-99, ATD

[56] References Cited UNITED STATES PATENTS 2,425,209 8/1947 Snyder etal. 277/96 2,433,589 12/1947 Adams 277/96X 2,447,930 8/1948 Biggs277/96X FOREIGN PATENTS 735,250 8/1955 Great Britain 277/96 PrimaryExaminer-Laverne D. Geiger Assistant Examiner.leffrey S. M ednickAttorney-Theodore B. Roessel ABSTRACT: A corrosion resistant, wearresistant, glass coated seal face is disclosed wherein the glass coatingis characterized by having a plurality of randomly scattered,nonconnecting, lubricant receiving voids therein which serve to receiveand retain lubricant particles deposited within the voids.

PATEINED [1EB29 I976 ISM FIG. 1

INVENTORS DONALD H. HALL jgwm J. NUNLIST FIG. 2

ATTQRNEY WEAR RESISTANT ARTICLES AND FACINGS THEREFOR :This applicationis a continuation of Ser. No. 441,624, filed Mar. 22, 1965, nowabandoned.

This invention relates to wear resistant articles and facings therefor,as well as a method for producing said facing, and more particularlyrelates to surfaces suitable for use as seal faces in mechanical seals.

In industries where large amounts of fluid are processed in containersor moved by pumps, it is common to provide devices having rotatingshafts that extend into fluid containing vessels. It is often necessaryto seal the openings, through which the rotating shafts enter thevessels, to prevent the leakage of fluids, fumes or lubricants. Stuffingboxes or mechanical seals are widely used for this purpose.

Mechanical seals have gained increased acceptance as the preferabledevice for such uses, as they provide a more effective seal and do notrequire repeated adjustments. However, mechanical seals include partsthat are constantly subjected to sliding friction and eventually wear toa degree that necessitates replacement. Repair or replacement of theseals is a costly and time consuming procedure that often requires ashutdown of the entire process. Therefore, it is desirable to in creasethe operating life of the components within the mechanical seal.

A mechanical seal, more particularly described hereinafter, comprises arotating portion, a stationary portion, a springloading device andstatic sealing means that stop leakage between the shaft and therotating seal ring, which are stationary relative to each other. Therotating portion and the stationary portion have highly finishedsurfaces that abut each other and are kept in contact by the forceexerted by the spring-loading device.

A commonly employed embodiment of a mechanical seal utilizes astationary seal seat fabricated from a corrosion resistant alloy orceramic material, and a rotating seal head fabricated from a relativelysoft noncorrosive material such as graphite, Teflon, etc. The matingsurfaces of the rotating and stationary portions are generally selectedof compatible materials to achieve low friction, long wear and corrosionresistance.

In the selection of materials for use in the mating portions of seals,ceramic materials have been quite popular because of their excellentwear resistance properties and corrosion resistance. However, thebrittleness and general susceptibility. of ceramic materials to thermalshock are major limitations. Historically, many ceramic seal rings arebroken both during production and the assembly procedure and others failin service. when the shaft to be sealed hits the ring. The thermal shockproperties are poor because of the inherently low heatconductivity ofceramic materials.

Ceramic coating coatings on metal substrates have been proposed as theideal solution to the above problems as the ceramic portion shouldprovide corrosion resistance and wear resistance and the metal substrateshould provide ease of fabrication, and better heat conductivity.However, ceramic coatings, which may be applied by welding rod or spraytechniques have not achieved widespread usage, as homogeneousand'dependable coatings are not easily obtained and high wear rates ofthe mating parts are often encountered. Further, such ceramic materialscontain connecting pores that provide a direct passage from the surfaceto the substrate and, therefore, do not protect the metal substratesfrom corrosive media.

:Glass coatings on a metal substrate would seem to provide anadvantageous material. Although the glass separately is relativelybrittle and a poor heat conductor, when a thin layer is applied to arnetalsubstrate, the properties of the composite article willsubstantially approximate those of the metal substrate. Glass coatingsare easily applied by well-known enameling techniques and are standardmaterials for corrosion resistant uses. Although homogeneous glass isgenerally weaker in tension than solid ceramics, after chipping of aglass coating the metal substrate remains capable of partly performingthe function of the total part. In contrast, the failure of a solidceramic part is often a catastrophic event that may cause an immediateloss of the fluid medium that is being sealed. It is thus apparent thatglass-coated metals have inherent advantages that would suggest theirsuitability for use in mechanical seals. However, glass-coatedmetalshave not been used, because in spite of the excellent corrosionresistance and the minimization of the physical shortcomings by the useof a metal substrate, glass surfaces have not exhibited sufficient wearresistance to justify their use in commercial applications.

It is accordingly the primary object of. this invention to providewear-resistant glasses suitable foruse as enamel coatings.

Recently, new partially-crystallized glass-ceramic coating materialshave been developed that provide improved physical and mechanicalproperties such as resistance to thermal shock and impact, corrosionresistance, thermal conductivity, and thermal stability at higheroperating temperatures than conventional enameling materials. Theseproperties would indicate that such materials would be well suited foruse as facings for the seal seats and heads in mechanical seals. I-Iow-.ever, our attempts to use partially crystallized glasses as enamels forseal rings wei'e unsuccessful as the rings failed at relative velocitiesgreater than 15 ft. per second. This failure occurred because of theexcessive heat that resulted from frictional forces generated by thesliding contact between the seal face and the seal seat. J

It is accordingly another object of this invention to provide a sealface material formed from a partially crystallized glass havingincreased wear properties and capable of minimizing the frictional heatdeveloped at highspeeds.

We have found that when a relatively soft surface, such as graphite, isin sliding contact with a harder surface, such as ceramic material, areduction of friction is effected by the lubricating action of particlesworn from the softer surface. This lubricating action occurs where theparticles from the softer surfacedeposit on the harder surface and thusdecrease the area of direct contact between the softer and hardersurfaces. However, for this deposit to adhere to the harder surface itmust have discontinuities on which the softer particles can anchor. In aseal face, a primary requirement is therelative smoothness and flatnessof the surface. To achieve the requisite surface properties, theabutting surfaces are commonly precision lapped to withinthree'lightband flatness and four microinches RMS of roughness. It is'anobject of this invention to provide a surface, characterized bysufficient flatness and smoothness to operate as a sea] face, yet havingvoids on the surface to facilitate the anchoring of particles erodedfrom a softer surface.

In mechanical seals the abutting sealing surfaces are usually held incontact by preloading. In such. cases loss of surface caused by wear iscompensated for by the pressure of the springs so that a self-adjustingaction is obtained. If the seal face is surface treated to provide thedesirable voids, the gradual wearing down of the surface will eventuallynullify the effect of the surface treatment. At this point, the rate ofwear will sharply increase thus accelerating the time for replacement ofthe seal. It is thus desirable and an object of this invention toprovide a glass or glass-ceramic body so structured that the surfacewill continuously exhibit discontinuities, notwithstanding the gradualwearing down of the body itself.

In providing a seal face that will constantly exhibit a surface withdiscontinuities it is important that the structural changes do notadversely affect the outstanding properties of wear resistance andcorrosion resistance that are peculiar to the basic materials. It isthus necessary to achieve the above-discussed discontinuities withoutforming passages from the surface to the substrate. Further, it is ofthe utmost importance not to increase the susceptibility to thermalshock. it is, therefore, an object of this invention to provide a methodfor providing said surface discontinuities without adversely affectingthe inherent physical properties of the base material.

We have found that the objects of this invention are attained by addingto a basic glass formulation materials that FIG. I is a side elevationalview partly in section of fluid agitation equipment embodying amechanical seal.

FIG. 2 is an approximately lOOXgraphic showing of a photomicrograph of acrystallized glass prepared according to the invention.

Referring to FIG. I, a vessel 2 is provided with an agitator shaft 4driven by a motor or other driving means (not shown) extending intovessel 2 through a flanged nozzle 8. The shaft 4 terminates in animpeller or mixing means (not shown).

A mechanical seal, generally designated at 12, surrounds the agitatorshaft 4 and comprises a stationary seal seat 14, a rotating seal head 16and spring assembly 18. Rotating seal head 16 has a highly finishedsurface that abuts a similarly finished surface of stationary seal seat14. Seal seat 14 has a glass or glass-ceramic coating 15. A springretaining member is fastened to the rotating shaft by setscrews ll.Stationary seal seat 14 is clamped into position by seal housing andspring assembly 18 through preloading holds seal head 16 into contactwith seal seat 14. A static sealing means 22 (O-ring or wedged Teflonmember) is provided to seal between shaft 4 and seal head 16, which aresubstantially static relative to each other.

In operation, sealing between the rotating head 16 and the stationaryseat 14 is effected by the intimate contact between the highly finishedfaces of these components caused by the spring loading of springassembly 18.

The present invention is specifically directed to providing a glass orglass-ceramic material suitable for use as a face material within theabove described structure.

FIG. 2 shows a glass matrix having a plurality of nonconnecting voids ordiscontinuities some of which intersect the surface.

The following specific examples will illustrate the manner in which theobjects of this invention are obtained.

EXAMPLE l A glass frit was formed having the following oxidecomposition:

SiO 57.3

TiO -8.8

SrO2.8

100 parts of the frit were milled with:

Parts carbonaceous silicate (99% SiO 4. 0 Beutouite O. 4 Enameling clay4. 0 Potassium chloride 0. 62 Sodium nitrate 0. 21 Silica 5. 0 Water 45.0

The above mixture was sprayed onto a mild steel substrate,

fired at l620 F. and then heat-treated for 1% hours 0 l440 F.

The resulting product was sectioned and disclosed a partiallycrystallized glass having a plurality of randomly distributednonconnecting cavities or voids therein, graphically shown in FIG. 2.

EXAMPLE ll parts of the same frit formed in Example I were milled with:

20 parts SiO 8 parts Enameling Clay 4 parts A 1. 0 0.4 parts Borax 0.5parts MgCO 0.25 parts NaNO 1.5 pans LiF 61 parts H 0 The above mixturewas sprayed onto a metal substrate. fired at 1620" F. and heat-treatedfor l /2hours 0 l440 F.

The product was sectioned and a photomicrograph of the resulting productrevealed a product similar to that of Example 1.

EXAMPLE ill The glass composition of Example I was applied to the faceof a seal ring within a mechanical seal according to the invention. Aglass composition, the same in all respects except for the absence ofvolatile compounds was applied to another seal ring. The ring coatedaccording to the invention was still performing satisfactorily after 6months of continual use. The ring prepared according to conventionaltechniques failed after 4 hours.

Although we have described the subject of this invention in terms of itsutility as a seal face, it is not limited thereto and is useful in manyother applications where wear resistance is necessary. For example, inthe textile industry, where fibers are passed at high speeds overvarious parts, a glass composition with an organic flocculating agentadded in accordance with our invention, increased the useful life of apart from 3 days to 3 months, and even longer in some cases.

To obtain the desired discontinuities within the coating, it isnecessary to add materials that volatilize during the firing, yet do notadversely affect the crystallization of the glass, such as by inhibitingcrystallization or causing premature crystallization. Further, thebubbles formed must not coalesce and grow during heat treatments to formconnecting pinholes in the coating which communicate with the base.Lastly, the materials should not be of a type that may spoil after agingseveral days or weeks in the milled slip.

We have found that carbonaceous silicate materials are suitable for usein forming the discontinuities that are the object of this invention.However, numerous available organic and inorganic materials such asclays, lithium fluorides, and organics may be useful for this purpose.In fact, any material that will volatilize during the maturing of thecoatings and that does not inhibit crystallization, form crystals, actas a nucleating agent or reduce corrosion resistance would be suitable.

To achieve the object of the invention it is necessary for thebubble-forming material to volatilize, yet remain entrapped within thematrix of the glass. Accordingly, volatilization must occur while theglass is sufficiently viscous to overcome the pressures exerted by thevolatilizing gases thereby preventing their escape and favoring thefonnation of bubbles. The softening point of the glass defines the lowerlimit at which the glass viscosity will favor the entrapment of bubbles.The upper limit is not definite but may be broadly characterized as thetemperature at which the glass would become sufficiently fluid to permitthe escape of the volatile materials. The range of temperatures definedby the softening point and this extremely fluid condition is generallyl00O F. to 1700 F.

Numerous have been tried or used as seal faces in mechanical seals.Porous materials, such as sintered brass and powdered metals aresuitable for some applications, however, such materials lack thecorrosion resistance necessary for many other applications. Solidceramic bodies offer better corrosion resistance than metals, but arerelatively fragile and expensive. Satisfactory ceramic coated metals arenot readily available because of the difficulties inherent in attemptingto provide a bond between the ceramic and the metal sufficiently strongto withstand the forces generated in use. Glass-coated metals haveheretofore provided the necessary corrosion resistance, but prior to thepresent invention have not been suitable because of the wear rate of thesurface.

The major advantage of this invention is the provision of glass coatingshaving in combination all the advantages of the prior glass andglass-ceramic coated materials and, in additiqm h i hitfiafore ytyeilahl w a res staa i Although the surface characteristics necessary toprovide increased wear resistance may be achieved by a surface treatmentsuch as etching or sandblasting, the preferred method is the fonnationof discontinuities throughout the face material.

This has the additional advantage of providing a wear resistant surfaceduring the entire life of the face material.

The term glass as used herein should be construed as including bothamorphous and crystallized, or semicrystalline glasses.

To assure good adhesion between various base metals and glass coatings,an expedient well-known in the art is the application of a ground coatenamel upon the surface of the metal. Ground coats are speciallyformulated to enhance uniform coating over the base metal and to form astrong bond between the surface or cover coat and the base metal. Afterthe aforesaid ground coat has been applied one or more cover coats areapplied thereover. These cover coats are formulated to provide thesurface characteristics required for the particular application. The useof ground coats and cover coats, both amorphous and semicrystalline, iswithin the scope of this invention.

Although we have disclosed specific methods, compositions and milladditions effective for the practice of our invention, it

, should be understood that the invention does not reside face; andproviding said voids without destroying the advantageous properties ofthe glass or glass-ceramic matrix.

Accordingly, the specific examples and materials are illustrative,rather than limiting, and those skilled in the art, in the light of thisdisclosure will be able to determine the specific parameters andmaterials that will most effectively suit their requiremgnts withoutdeparting from the spirit and scope of the invention as set forth in theappended claims.

We claim:

1. A rotating shaft seal assembly comprising:

a. a rotating seal member surrounding the shaft;

b. sealing means between said rotating shaft and member;

c. a stationary seal member having a seat in sliding, fluid tightcontact with said rotating seal member;

d. bias means for urging said rotating seal member in fluid tightcontact with said stationary seal seat;

e. one of said seal members having a coating of glass formed thereon,said coating formed with a plurality of randomly scattered,nonconnecting, bubbles, a portion of said bubbles being wholly containedwithin said coating and said coating having a ground planar wearingsurface formed thereon to expose a portion of said. bubbles, saidexposed bubbles providing lubricant receiving voids in said coating; and

f. the other of said seal members being formed of a softer material thanthe planar surface of said glass coated seal face said softer materialserving to wear off in particles and deposit in'said voids while insliding, fluid tight contact with said glass-coated seal, therebylubricating and increasing life of the seal assembly and the glasscoated seal face gradually wearing in service to expose additionalbubbles.

2. The seal assembly as defined in claim 1, wherein said coating ofglass is formed on said stationary seal member.

3. The seal assembly as defined in claim 2, wherein said glass coatingis formed from a crystallizable glass.

4. The seal assembly as defined in claim 3, wherein said rotating sealmember is formed of graphite.

SQThe seal assembly as defined in claim 1, wherein said coating of glasscomprises an impervious ground coat and a pervious cover coat.

